of the Fishery Board for Scotland. 



29 



The Grudie a Late River : Cause of its Lateness. — The Grudie is a later 

 river than any of those that run into the Pentland Firth to the east of 

 it. Indeed, it may be said that with it the late rivers begin ; as all the 

 rivers westward from it to Cape Wrath, and southward from Cape Wrath 

 along the West Coast of Scotland and up to the head of the Scotch shore 

 of the Solway Firth, and in the Inner and Outer Hebrides, are, with 

 scarcely an exception, late ; whereas, almost all the rivers eastward of the 

 Grudie, between it and Duncansby Head, and southwards between Dun- 

 cansby Head and the Tweed are early. The cause of this lateness or 

 earliness I believe to arise from the relative temperatures of the fresh 

 water of the rivers, and of the sea into which they fall. I stated this 

 theory in letters to the Scotsman in October and November 1875; and 

 afterwards more fully in my Treatise on Salmon Fisheries, in Stanford's 

 series of British Industries, and in the Journal of the Scottish Meteorological 

 Society in 1878. The Scottish rivers running into the German Ocean 

 are almost all early rivers. They have comparatively long courses, and 

 fall into the sea at considerable distances from their mountain sources, 

 after running during some part of their career through districts not greatly 

 elevated and possessing a moderate climate. But the German Ocean, 

 into which these rivers flow, is a cold sea ; and in winter and early spring 

 the river temperature is, in ordinary seasons, probably higher than that 

 of the sea, and therefore salmon ascend these rivers early in the season. 

 Take the Tay, for example. It is well known,, that salmon run into it in 

 great numbers in the months of December and January, so that, when 

 the fishing begins in February, Loch Tay is stocked with clean and heavy 

 salmon. On the West Coast, on the other hand, the rivers that fall into 

 the Atlantic are nearly all late. They have short courses, and their 

 fountain heads are much tilted up, as they rise in that lofty and singularly 

 picturesque chain of mountains which, beginning not far from Cape 

 Wrath, skirts the shores of Sutherlandshire, Ross-shire, and Inverness- 

 shire for more than 100 miles, at distances varying from 5 to 20 miles 

 from the western sea. In winter and spring, and sometimes even in early 

 summer, these mountains are snow-clad or partly covered with snow, and 

 every partial melting of their snows brings down torrents of ice-cold 

 water, which rush through the short channels of these rivers into the sea. 

 But the water of that sea, unlike that of the German Ocean that washes 

 our eastern coasts, is warmed by the soft influence of the Gulf Stream, 

 and the salmon, consequently, prefer to remain in it until the snow water 

 has run off, and the milder weather of June and July has raised the 

 temperature of the river waters, and then they begin to ascend. In order 

 to test the correctness of the theory above stated, careful and prolonged 

 observations on the relative temperatures of several late and early rivers, 

 and of the sea into which they flow, would be necessary. A very ingenious 

 apparatus was devised by the late Thomas Stevenson, C.E., and figured 

 and described in the Journal of the Scottish Meteorological Society, for 

 observations of sea and river temperatures by means of thermometers 

 continuously immersed. If the result of such observations, carried on for 

 a sufficient length of time, should be to prove the correctness of the theory 

 above stated, we should obtain something approaching to a scientific 

 method of determining the annual close-time suitable for each river. 

 Another result would be to prove the futility of all attempts to change late 

 rivers into early ones by stocking them with salmon bred from ova taken 

 from early rivers. For, if the theory with regard to the constant and 

 invariable effects of the relative temperatures of the sea, and of the rivers 

 which fall into it, upon the earliness or lateness of the ascent of salmon 

 be correct, it seems quite clear that all such attempts are a mere waste of 



